When linking a particular iOS app project to a static framework, Xcode is reporting duplicate symbol errors from within the single static framework file (although the duplicates are reported sourced from different object files within that framework):
duplicate symbol _kMGLMinimalViewport in:
/Users/alex/Documents/Code/MyProject/ThirdParty/MetalGL-0.9.0/MetalGL/MetalGL.framework/MetalGL(MGLContext.o)
/Users/alex/Documents/Code/MyProject/ThirdParty/MetalGL-0.9.0/MetalGL/MetalGL.framework/MetalGL(MGLRenderPipelineState.o)
The _kMGLMinimalViewport symbol being reported as duplicate is a struct that is declared and defined within a header file within the source code of the framework:
MGLPixelRect kMGLMinimalViewport = (MGLPixelRect){0, 0, 0, 0};
which is then #imported into several implementation files within the framework source, including both .m files and inline functions within other .h files. The symbol is used strictly internally within the framework and the declaration is not even visible to the final app project as part of a visible header file.
Confusingly, this duplicate error does not appear when linking this framework to other app projects, but I can't find any reason why this particular app project is reporting an error when linking this framework.